The proposed studies involved further investigations into the biochemical effects of amphetamine and ring-substituted derivatives, with particular emphasis on p-chloroamphetamine (PCA) and fenfluramine. These drugs are of potential value as biochemical tools in clinical and preclinical studies as therapeutic agents in the treatment of depression and obesity. Therefore, it is critical that their biochemical effects in laboratory animals be understood. PCA causes an immediate, marked decrease in the levels of serotonin and tryptophan hydroxylase activity in the brains of rats, which lasts for several months after a single dose. A principal objective of the proposed research is an elucidation of the mechanism(s) of the initial, reversible and the long-term, toxic effects of PCA on serotonergic neurons in the brains of laboratory animals. The role of an active metabolite will be examined. Studies of different species and doses and the development of PCA sensitivity in immature rats are planned. A detailed examination of the metabolic fate of 14C-PCA in rats and mice may permit the identification of an active metabolite responsible for the toxic effects of PCA. Following purification and characterization of urinary metabolites by solvent extraction, thin-layer and high-pressure liquid chromatography, final identification worked out, these techniques will be applied to specific tissues, in particular, brain and liver. Biochemical studies of the apparent differences in the action of PCA and fenfluramine are planned. The long-term (toxic) biochemical effects of continuous exposure of rats and mice to amphetamine and related compounds will be investigated. In structure-activity studies, the potency and selectivity to induce toxic effects after continuous administration will be compared with in vitro potency as amine uptake inhibitors and releasing agents. In-depth studies of amphetamine will examine several parameters of amine function and the role of active metabolites in the long-term effects produced by this CNS stimulant.